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EBT2 film as a depth‐dose measurement tool for radiotherapy beams over a wide range of energies and modalities
Author(s) -
Arjomandy Bijan,
Tailor Ramesh,
Zhao Li,
Devic Slobodan
Publication year - 2012
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3678989
Subject(s) - ionization chamber , materials science , bragg peak , scanner , dosimetry , dose profile , range (aeronautics) , optics , beam (structure) , proton , ionization , radiation , dosimeter , nuclear medicine , physics , ion , nuclear physics , medicine , quantum mechanics , composite material
Purpose: One of the fundamental parameters used for dose calculation is percentage depth‐dose, generally measured employing ionization chambers. There are situations where use of ion chambers for measuring depth‐doses is difficult or problematic. In such cases, radiochromic film might be an alternative. The EBT‐2 model GAFCHROMIC™ film was investigated as a potential tool for depth‐dose measurement in radiotherapy beams over a broad range of energies and modalities. Methods: Pieces of the EBT‐2 model GAFCHROMIC™ EBT2 film were exposed to x‐ray, electron, and proton beams used in radiotherapy. The beams employed for this study included kilovoltage x‐rays (75 kVp), 60 Co gamma‐rays, megavoltage x‐rays (18 MV), electrons (7 and 20 MeV), and pristine Bragg‐peak proton beams (126 and 152 MeV). At each beam quality, film response was measured over the dose range of 0.4–8.0 Gy, which corresponds to optical densities ranging from 0.05 to 0.4 measured with a flat‐bed document scanner. To assess precision in depth‐dose measurements with the EBT‐2 model GAFCHROMIC™ film, uncertainty in measured optical density was investigated with respect to variation in film‐to‐film and scanner‐bed uniformity. Results: For most beams, percentage depth‐doses measured with the EBT‐2 model GAFCHROMIC™ film show an excellent agreement with those measured with ion chambers. Some discrepancies are observed in case of (i) kilovoltage x‐rays at larger depths due to beam‐hardening, and (ii) proton beams around Bragg‐peak due to quenching effects. For these beams, an empirical polynomial correction produces better agreement with ion‐chamber data. Conclusions: The EBT‐2 model GAFCHROMIC™ film is an excellent secondary dosimeter for measurement of percentage depth‐doses for a broad range of beam qualities and modalities used in radiotherapy. It offers an easy and efficient way to measure beam depth‐dose data with a high spatial resolution.